Electric lamp for projection apparatus



J. E. RANDALL AND L. T. RESER.

ELECTRIC LAMP FOR PROJECTINGAPPARATUS. APPLICATION FILED JAN-15,1917.

Patented Nov- 2,1920.

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H -W4@M UNITED STATES PATENT OFFICE.

JOHN E. RANDALL, 01E CLEVELAND, OHIO, AND LEROY T. RESER, OF BALDWIN, KANSAS, ASSIGNORS T GENERAL ELECTRIC GO IV IPANY, A CORPORATION OF NEW YORK.

ELECTRIC LAMP FOR PROJECTION APPARATUS.

Specification of Iitters Patent. 7 Patented NOV. 2,

Application filed January 15,. 1917. Serial No. 142,373.

To all whom it may concern:

Be it knownlthat we, JOHN E. RAN ALL, a citizenof the United States, residing at Cleveland, Cuyahoga county, Ohio, and Ln- ROY T. Rnsnn, a citizen of the United States, residing at Baldwin, Douglas county, Kansas, have invented new and useful Improvements in Electric Lamps for Projection Apfparatus, of which the following is a speciv fioation.

Qurinvention relates to projection apparatus of various kinds including stereopticon, 'fiood lighting and moving picture reproduction apparatus and more especially to an electric incandescent filament lamp particularly adapted for use with such apparatus.

One object of our invention is a lamp which will give a beam of light uniform throughout itsdepth. Another object is a lamp whose intrinsic brilliancy is greater than that of prior lamps having equal power consumption and the same operating temperature. Further objects are the elimination of local heating and arcing in the filament coils, and the simplification of the ratus.

All)

The incandescent filament, lamp, as hitherto known, has not been particularly adapted for use as a source of light in moving picture projection apparatus, clue among other things, to lack of intensity and lack of uniformity 1n light production throughout the filament area. Of the commercial lamps in use the gas filled tungsten lamp may be operated at the highest known temperature and efficiency, but prior lamps of this type have certain disadvantages when used in applications of this kind. For instance,- the light production and emission arenon-uniform in character and to obviate the objection the filament has been arranged in grid form, the sections being connected. in series.

This grid arrangement, while an improvement, failed to entirely remove this difiiculty and in order to further increase the uniformity in light production and distribution, it has been proposed to employa reflector or mirror (spherical), located back of the lamp, for projecting an image ofthe filament adjacent thereto and within the filament plane, thereby bridging the gaps between adjacent sections of the ser1esconnected filaments and practicall doubling the area of the light soiirce. e have found thismrrangement to be objectionable from an operative standpoino on account of the difficulties in making accurate adjustments of the lamp with reference to the mirror and lenses. rMoreover the refiected image is less intense than the original light source and this gives rise to uneven illumination on the screen. For instance,

the intensity of the light issuing from the reflected image has been found to bev approximately only 40% of the intensity of light issuing from the original light source. Furthermore I have found that thelife of the lamp is shortened and its operation impaired when the mirror or reflector is used. This is probably .due to aggravated local heating of the filament brought about by the presence of the mirror or reflector. Moreover the series-connected and grid formed filaments of the prior art have a tendency to are across from one filament to the other,

,oftentimes before the lamp has had a reasonably long useful life, the arcing being aggravated by the high temperature at which the filament is operated. -Furthermore, the potential difference between the coils in adjacent filament sections probably give rise to discharge or cross currents be tween these adj aoent coils which are thought to cause a gradual impairment of the filar ment by the evaporation of the tungsten at certain points of the filament. These discharge currents are probably increased and the consequent deterioration of the filament is aggravated by the high tem erature and high efiiciency at which the fi ament must be operated to give the. required illumination intensity. -4 All of these causes contributeto premature termination of the useful life of the seriesconnected and gridformed filament lamps.

In accordance with our invention 'we redues to a minimum or entirely remove these causes (for premature termination of the lOt useful life and we do away altogether with.

the necessity of a reflector or mirror for increasing the intensity and the uniformity of thelight beam, thereby saving the expense of refiectorinstallation and avoiding the.

' plane incandescent lamp, which gives a highly intense and uniform beam of light and whose life is not unduly impaired by arcing and cross currents and by its high temperature in operation. Our improved lamp embodies more specifically a multiplicity of coiled. or spiral filaments connected in multiple and these filaments are mounted close together in panel form on two rigid electro-conductive posts or supports, the filament sections and the supports being easily disposed and assembled in a monoplane position. With the multiple connection the adjacent, coils on the different filaments are at the same potential and consequently there is no tendency to are across from one filament to another and moreover the discharge or cross currents which are thought to attack the tungsten filament are reduced to a minimum. The filaments may, therefore, be brought close together, or even crowded together to form a true ribbon filament which gives ahighly intense and uniform light beam throughout its area.

. We have foundtoo that the intrinsic brilliancy of the parallel connected coils disposed closely together is substantially greater than that of the series-connected and grid-formed filaments of the prior art,

giving the appearance of a higher tempera ture, although the power consumption in the two cases is the same. By this higher intrinsic brilliancy the illumination efiiciency is greatly enhanced. This higher brilliancy is probably due to'radiation added by reflections between the filaments.

Another important feature of our inven-.

tion is that by concentrating the filament sections the whole plane of the filaments may be brought within the field of the screen illumination, thereby making use of every turn of the filament sections to fur nish useful light. With the old series-connected filamentssuch concentration was impossible and consequently alamp embodying picture reproduction apparatus where standardization has been pretty generally accomplished.

Another important feature of our invention resides in theavoidance of certain difficulties experienced in making accurate focal adjustments with the lamps of the prior art. We have found these difficulties to be due in part to the displacement of the filament sections out of the monoplane position. This displacement may be due either to. inaccurate adjustments in the manufacture or to subsequent distortion and s agging in the operation of the lamp. The displacement during the manufacture of the prior lamps was the result of difiiculties experienced in accurately maintaining a monoplaneposition while shaping the filament into grid form and also while adjusting the multiplicity of supports necessary in this type of lamp. By mounting the filaments in panel form between the two posts or supports the positioning of the filaments in a monoplane position becomes a simple matter, as will hereafter more particularly appear. The distortion of the filament out of the monoplane position may be due to the twisting of the coil filaments under the influence of the intense heat of the lamp. .l/Ve have found, however, that alldisplacement due to distortion or'sagging may be obviated by accurately predetermining the maximum length of the filaments for certain wire and coil diameters and rigidly supporting these filament sections from their ends, as, for instance, mounting them on the parallel disposed rigid electro-conductive posts. For. instance, with a wire diameter of .0195 inches and a coil diameter of approximately .08 inches, we have found that a filament section one-half inch long from end coil to end'coil ismaintained in the monoplane position at all times and no. appreciable distortion or sagging takes place in the operation, notwithstanding the intense heat of the filament. The length. of the filament may be increased by 25 to 50% without unduly increasing the sagging or distortion.

The above features set forth as characterizing our novel lamp make it partioularly adaptable for use in moving picture reprodue-tion apparatus. For instance, with the f filament lengths closely coiled and assembled together as above noted, the light emitted is substantially uniform throughout the depth ofthe beamand the'curve of distribution approximates that of a solid band of light. Assuming an optical system is employed which transmits to the screen the light flux within a solid angle of 110 degrees,

ximately 25% of the total light mitted by the source is useful in lighting the screen, which compares favorably with the calculated 30 to 33% useful light expected from a solid band source of the same monoplane area, the useful light in the latter case being dependent on the thickness of the assumed band of tungsten. The 33% useful light would be expected if no thick ness is assumed, and the 25% useful light is obtained with four coils arranged in multiple, the coils being .08 inch in diameter and -should be concentrated into a monoplane' inch long. The closely coiled filaments with moving picture apparatus now in use and the best results are obtained when the concentration is such that the length of the monoplane area is less than twice the breadth. For example, with-four filament lengths of the above noted dimensions, closely coiled (turns separated by approxi mately one thirty second of an inch) and assembled together'in a monoplane area of approximately sixteen one hundredths of a square inch (five tenths of an inch long by thirty-two one hundredths inches wide) and with a calculated operating temperature of approximately 3275 degrees K (absolute), a spherical candle power of 1950 or greater has been obtained and the intensity at right angles to the plane of the source has reached 3350 candle power, and tests have shown a uniform intensity of six to ten foot candles on a screen at an eighty foot throw, these results being obtained without the use of a mirror or reflecton. The tests were made on lamps operating at approximately 12' volts and at an overall efiiciency greater than j one-half watt ,per candle, the leading-in and supports; Fig. 3 shows a diagrammatic illustration of the lamp and moving picture apparatus; and Fig. 1 is a partial elevation of another modifying construction-of the filament.

The preferred construction is shown in Fig. 1 where the usual 'inclosing bulb 1 is used to house the lamp filament and leadingin wires and supports. The supports 2 which may be. of nickel or other metals extend upwardly from the stem and carry the coiled filaments 3. The latter are preferably carried on auxiliary supports 4, as of tungsten or molybdenum, which are securely fastened to the lowersupports in any convenient manner, as by welding. The filaments 3 may be easily and quickly secured to the supports by forming electrical welds between the filament ends and the posts 4. The auxiliary supports or posts 4- and filaments 3 may be assembled and mounted as p a unit on supports 2, or the posts 4: may be accurately mounted and positioned in the same plane Without the exercise of great care, andthe filaments subsequently mounted. A convenient way of mounting the filamerits is to assemble the filaments between suitable clamps and in a monopla'ne position and then, causing the filaments so assembled to bridge the sup-portsv 4c, securely weld the free ends to'the posts by resistance or are welds. The supports should be of large and substantial dimensions as compared with the filaments, that is, they should have such a rigidity as not to yield to any strain'of the filaments during the operation. The rigidity and strength of the supports combined with. the comparatively short filaments (length inch, wire diameter .0195 and coil diameter .08 inch) avoid any harmful displacement during the normal life of the lamps and this renders the making of focal adjustments a simple and more certain matter. The filament 3, as shown in the drawin'gs, may be actually crowded together without causing any inconvenience from arcing, the coils of adjacent filaments being substantially at the same potential. Each filament in the embodiment shown takes approximately 20 amperes running at 12 volts across the lamp terminals and at this 'efiiciency the life is from 100 to150 hours.

Fig. 2 shows a construction wherein the filaments are arranged at right angles to the position illustrated in Fig. 1, the con-,

struction otherwise being substantially the same.

nection with moving picture apparatus, wherein ,are shown a condensing lens 5, an objective 6, film 7 and screen 8. The usual mirror or reflector is entirely done away with, and the installation expense is thereby saved. Moreover, the necessary accurate ad justments accompanying the mirror are en tirely obviated, and the harmful results on the life of the lamp are eliminated.

What we claimas new and desire to secure by Letters Patent of the United States is:

In Fig. 3 the lamp is illustrated in con- 1. An electric incandescent lamp comprising a plurality of closely coiled filaments of uniform cross section disposed closely together and connected in multiple, the distance between adjacent filaments being substantially less than the diameter of the filament coil. a 2. An electric incandescent lamp comprising a" multiplicity of coiled filaments of uniform cross section arranged parallel to each other in a plane and electrically connected in multiple, the distance between adjacent filaments being substantially less than the diameter of the filament coil.

3. An electric incandescent lamp comprising a multiplicity of closely coiled filaments of uniform cross section arranged in a plane jacent filaments being substantially less ments being substantially parallel to each other and electrically connected in multiple, the distance between adthan the diameter of the filament coil.

4. An electric incandescent lamp comprising two or more coiled filaments of uniform cross section disposed closely together in one plane and electrically connected in partween adjacent filaments being substantially less than the diameter of the filament coil. 6. An electric incandescent lamp comprising a multiplicity of --coiled filaments of uniform cross section carried and supported at their ends by two parallel and electroconductive posts, the distance between adjacent filaments being substantially less than the diameter of the filament coil.

7. An electric incandescent lamp particularly adapted for use in projection apparatus comprising two rigid electro-conduce tive posts mounted upon the stem and a multiplicity of closely coiled filaments of uniform cross section bridging said posts and disposed closely together in one plane,

the distance between adjacent filaments being substantially less than the diameter of the filament" coil. p

8. Arr-electric incandescent lamp particularly adapted for use in projection apparatus comprising two rigid electro-conductive posts parallel arranged and mounted upon the stem and multiplicity of closely coiled filaments of. uniform cross section bridging said posts and disposed closely together, the distance between adjacent filaj ments being substantially less than the diameter of the filamentcoil.

9; An electric incandescent lamp for projection' purposes comprising a plurality of closely coiled metal filaments of uniform cross section connected in parallel and disposed substantially in a single plane and operatingtmt an efficiency greater than onehalf watt per candle power, the distance between adjacent filaments being substantially less than the diameter of the filament coil.

10. An electric incandescent lamp for projection purposes comprising a plurality of connected in parallel and concentrated into a monoplane area of less than half a square inch, the length of said monoplane area being less than twice its breadth, the distance between adjacent filaments being substantially less than the diameter of the filament coil.

11. An electric incandescent lamp for projection purposes comprising a plurality of coiled metal filaments of uniform cross section electrically connected in parallel and operating at a temperature whichgives an efiiciency greater than one-half watt per candle, said filaments being concentrated to such extent and into a volume of such contourthat the light flux is substantially uni form throughout the depth of the beam and the curve of distribution approximates the curve of distribution of a solid band of light, the distance between adjacent fila- Inents being substantially less than the diameter of the filament coil. 12. In an electric incandescent projection lamp, a filament comprising a plurality of parallel closely wound coils connected electrically in-multiple and disposed in the same plane, the spaces between the said coils.

being materially less than the width or diameter of the said coils.

In witness whereof the said RANDALL has hereunto set his hand this 10th day of closely coiled metal filaments of uniform cross section electrically and geometrically January, 1917, and the said Russia has hereunto set his hand this 6th day of January, 1917.

\ JOHN E. RANDALL. LEROY T. RESER. 

